Network Node, User Equipment and Methods Therein for Adjusting the Transmit Timing of Uplink Transmissions

ABSTRACT

Methods and devices for adjusting timing of uplink transmissions to a network node in a telecommunications system are provided. A user equipment (“UE”) is configurable with more than one aggregated serving cells that are divided into one or more groups of serving cells based on a timing advance value. The one or more groups of serving cells each comprises a timing reference serving cell. The reception timing of a downlink transmission from a timing reference serving cell is used as an uplink timing reference for the timing reference serving cell. The UE determines a change to a second timing reference serving cell and applies an incremental adjustment of the transmit timing of uplink transmissions for the serving cells in the group of serving cells with respect to a timing reference based on the reception timing of a downlink transmission from the second timing reference serving cell in the UE.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/269,268, filed Sep. 19, 2016, which is a continuation of U.S. patentapplication Ser. No. 13/583,505, filed Sep. 7, 2012, now U.S. Pat. No.9,503,994, which is the National Stage of International Application No.PCT/SE2012/050692, filed Jun. 20, 2012, which claims the benefit of U.S.Provisional Application 61/595,856, filed Feb. 7, 2012, the disclosuresof each of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

Embodiments herein relate to a network node, a user equipment andmethods therein. In particular, embodiments herein relate to adjustingthe transmit timing of uplink transmissions in a telecommunicationssystem.

BACKGROUND

In today's radio communications networks a number of differenttechnologies are used, such as Long Term Evolution (LTE), LTE-Advanced,Wideband Code Division Multiple Access (WCDMA), Global System for Mobilecommunications/Enhanced Data rate for GSM Evolution (GSM/EDGE),Worldwide Interoperability for Microwave Access (WiMax), or Ultra MobileBroadband (UMB), just to mention a few possible technologies for radiocommunication. A radio communications network comprises radio basestations providing radio coverage over at least one respectivegeographical area forming a cell. The cell definition may alsoincorporate frequency bands used for transmissions, which means that twodifferent cells may cover the same geographical area but using differentfrequency bands. User equipments (UE) are served in the cells by therespective radio base station and are communicating with respectiveradio base station. The user equipments transmit data over an air orradio interface to the radio base stations in uplink (UL) transmissionsand the radio base stations transmit data over an air or radio interfaceto the user equipments in downlink (DL) transmissions.

LTE is a project within the 3rd Generation Partnership Project (3GPP) toevolve the WCDMA standard towards the fourth generation (4G) of mobiletelecommunication networks. In comparisons with third generation (3G)WCDMA, LTE provides increased capacity, much higher data peak rates andsignificantly improved latency numbers. For example, the LTEspecifications support downlink data peak rates up to 300 Mbps, uplinkdata peak rates of up to 75 Mbit/s and radio access network round-triptimes of less than 10 ms. In addition, LTE supports scalable carrierbandwidths from 20 MHz down to 1.4 MHz and supports both FrequencyDivision Duplex (FDD) and Time Division Duplex (TDD) operation.

LTE technology is a mobile broadband wireless communication technologyin which transmissions are sent using orthogonal frequency divisionmultiplexing (OFDM), wherein the transmissions are sent from basestations, also referred to herein as network nodes or eNBs, to mobilestations, also referred to herein as user equipments or UEs. Thetransmission OFDM splits the signal into multiple parallel sub-carriersin frequency.

A basic unit of transmission in LTE is a Resource Block (RB) which inits most common configuration comprises 12 subcarriers and 7 OFDMsymbols in one time slot. A unit of one subcarrier and 1 OFDM symbol isreferred to as a resource element (RE), as shown in FIG. 1. Thus, an RBcomprises 84 REs.

Accordingly, a basic LTE downlink physical resource may thus be seen asa time-frequency grid as illustrated in FIG. 1, where each ResourceElement (RE) corresponds to one OFDM subcarrier during one OFDM symbolinterval. A symbol interval comprises a cyclic prefix (cp), which cp isa prefixing of a symbol with a repetition of the end of the symbol toact as a guard band between symbols and/or facilitate frequency domainprocessing. Frequencies for subcarriers having a subcarrier spacing Δfare defined along an z-axis and symbols are defined along an x-axis.

In the time domain, LTE downlink transmissions are organized into radioframes of 10 ms, each radio frame comprising ten equally-sizedsub-frames, #0-#9, each with a T_(sub-frame)=1 ms of length in time asshown in FIG. 2. Furthermore, the resource allocation in LTE istypically described in terms of resource blocks, where a resource blockcorresponds to one slot of 0.5 ms in the time domain and 12 subcarriersin the frequency domain. Resource blocks are numbered in the frequencydomain, starting with resource block 0 from one end of the systembandwidth.

An LTE radio sub-frame is composed of multiple RBs in frequency with thenumber of RBs determining the bandwidth of the system and two slots intime, as shown in FIG. 3. Furthermore, the two RBs in a sub-frame thatare adjacent in time are denoted as an RB pair.

Downlink (DL) transmissions are dynamically scheduled, i.e. in eachsubframe the network node transmits control information about to whichuser equipments data is transmitted and upon which RBs the data istransmitted, in the current DL subframe. This control signalling istypically transmitted in the first 1, 2, 3 or 4 OFDM symbols in eachsubframe. The number n=1, 2, 3 or 4 is known as a Control FormatIndicator, CFI. The DL subframe also comprises common reference symbols,CRS. The CRS are known to the receiver and used for coherentdemodulation of e.g. the control information.

Carrier Aggregation

In LTE Release 10, a Component Carrier (CC) bandwidth of up to 20 MHz issupported. This is the maximal carrier bandwidth for the earlier LTERelease 8. Hence, an LTE Release 10 operation that is wider than 20 MHzis possible. To a UE of LTE Release 10, this may appear as a number ofLTE carriers.

However, it may also be advantageous to assure that an efficient use ofa wide carrier is also performed for legacy UEs, i.e. where legacy UEsmay be scheduled in all parts of the wideband LTE Release 10 carrier.One way to do is by means of Carrier Aggregation (CA), as shown in FIG.4.

In the LTE Release 10, up to 5 aggregated carriers is supported. Eachcarrier is limited in the Radio Frequency (RF) specifications to haveone out of six bandwidths, namely, 6, 15, 25, 50, 75 or 100 RBs. Thesecorrespond to 1.4, 3, 5, 10, 15 and 20 MHz, respectively.

The number of aggregated CCs, as well as, the bandwidth of theindividual CC may be different for UL and DL. A symmetric configurationrefers to the case where the number of CCs in DL and UL are the same. Anasymmetric configuration refers to the case where the number of CCs inDL and UL are different.

Note that the number of CCs configured in the network node may bedifferent from the number of CCs as seen by a UE. For example, a UE maysupport more DL CCs than UL CCs, even though the network node offers thesame number of UL CCs and DL CCs.

CCs may also be referred to as cells or serving cells. Particularly, inan LTE network, the CCs aggregated by a UE may be denoted Primary Cell(PCell) and Secondary Cells (SCells). The term “serving cell” maycomprise both a PCell and SCells. The PCell is UE specific and may beviewed as “more important”. That is because vital control signaling andother important signaling is typically handled via the PCell. The CCconfigured as the PCell is the primary CC, whereas all other CCs aresecondary CCs.

During initial access a UE of LTE Release 10 acts similarly to a UE ofLTE Release 8. For example, upon successful connection to the network aUE may, depending on its own capabilities and the networks capabilities,be configured with additional CCs in the UL and DL. This configurationmay be based on Radio Resource Control (RRC) signalling.

Because of heavy signalling and rather slow speed of the RRC signalling,a UE may be configured with multiple CCs, even though not all of the CCsare currently being used. If a UE is activated on multiple CCs, itfollows that the UE has to monitor all DL CCs, e.g. for a PhysicalDownlink Control Channel (PDCCH) and Physical Downlink Shared Channel(PDSCH). This implies a wider receiver bandwidth, higher sampling rates,etc. This will result in higher power consumption by the UE.

Timing Alignment of Signals Received at the Network Node

In order to preserve the orthogonality in UL, the UL transmissions frommultiple UEs need to be time aligned at the network node. This meansthat the transmit timing of the UEs, which are under the control of thesame network node, should be adjusted to ensure that their transmittedsignals arrives at the network node at the same time. More specifically,well within the Cyclic Prefix (CP). CP may e.g. be seen as a guardinterval for the symbols in the signals. This ensures that the networknode is able to use the same resources, i.e. the same DFT or FFTresource, to receive and process the signals from multiple UEs.

As shown in FIG. 5, UEs may be located at different distances from thenetwork node. In FIG. 5, the UE 522 is located closer to the networknode 510 than the UE 521. Because the UE 521 and the UE 522 are locatedat different distances from the network node 510, the UE 521 and the UE522 will need to initiate their UL transmissions at different times. AUE far from the network node 510, i.e. UE 521, needs to starttransmission earlier than a UE close to the network node 510, i.e. UE522. This may, for example, be handled by a Timing Advance (TA) of theUL transmission from different UEs. That is, a UE 521 may start its ULtransmission before a nominal time given by the timing of the DL signalthat was received by the UE 521.

The timing advance is further illustrated in FIG. 6. In FIG. 6, the ULtiming advance is maintained by the network node 510 through timingalignment commands to the UE 521 and the UE 522 based on measurements onUL transmissions from the UE 521 and the UE 522, respectively. Throughthese timing alignment commands, the UE 521 and the UE 522 arerespectively ordered to start their UL transmissions 530, 540 earlier orlater, such that the UL transmissions 530, 540 from the UE 521 and theUE 522 are time aligned at the network node 510.

This applies to all UL transmissions except for random access preambletransmissions on Physical Random Access Control Channel (PRACH), i.e.including transmissions on the Physical Uplink Shared CHannel (PUSCH),Physical Uplink Control CHannel (PUCCH), and Sounding Reference Signal(SRS). There is a strict relation between DL transmissions and thecorresponding UL transmissions. Examples of this are the timing betweena Downlink Shared CHannel (DL-SCH) transmission on PDSCH to the HybridARQ (HARQ) Acknowledgment/Non-Acknowledgment (ACK/NACK) feedbacktransmitted in UL, either on PUCCH or PUSCH, or the timing between an ULgrant transmission on PDCCH to the Uplink Shared CHannel (UL-SCH)transmission on PUSCH.

By increasing the timing advance value for a UE, the UE processing timebetween the DL transmission and the corresponding UL transmissiondecreases. For this reason, an upper limit on the maximum timing advancehas been defined by 3GPP in order to set a lower limit on the processingtime available for a UE. For LTE networks, this value has been set toapproximately 667us. This corresponds to a cell range of around 100 km.Note also that the timing advance value may compensate for the roundtrip delay.

In LTE Release 10, there is only a single timing advance value per UEand all UL cells are assumed to have the same transmission timing. Thereference point for the timing advance is the receive timing of theprimary DL cell.

In LTE Release 11, different serving cells used by the same UE may havedifferent timing advance values. In 3GPP, it is currently assumed thatserving cells sharing the same timing advance value, e.g. depending onthe deployment, will be configured by the network node to belong to atiming advance group, also referred to as a TA group.

It is further assumed that if at least one serving cell of the TA groupis time aligned, all serving cells belonging to the same TA group mayalso use this TA value. Thus, for example, to obtain time alignment foran SCell belonging to a different TA group than the PCell, it is thecurrent 3GPP assumption that initiated random access by the network nodemay be used to obtain an initial TA-value for this SCell; thus, also forthe TA group which the SCell belongs to. The reference point for the TAhas not been determined as of yet.

Timing Alignment of Signals Transmitted at the Network Node

There is a requirement on the network node to align the transmit timingof signals transmitted to the same UE by different transmitter ports orbranches. This requirement applies to frame timing in transmit (TX)diversity transmissions, MIMO transmission, carrier aggregation andtheir combinations e.g. antennas involved MIMO transmission, carrierfrequencies or cells involved in multi-carriers, CoMP, etc.

In general, for any specific set of transmitter configuration ortransmission mode in the network node, the Time Alignment Error (TAE) isdefined as the largest timing difference between any two transmittedsignals. The purpose of the TAE requirement is to ensure that the UEreceived signals within a certain period of time. This namely reducesthe processing and complexity in the UE. For example, in case of MIMO orTX diversity transmissions, at each carrier frequency, the TAE shall notexceed 65 ns. In another example, in case of intra-band contiguouscarrier aggregation, with or without MIMO or TX diversity, the TAE shallnot exceed 130 ns. For inter-band carrier aggregation, with or withoutMIMO or TX diversity, the TAE shall not exceed 1.3 μs. In a furtherexample, in case of CoMP or carrier aggregation when the cells orcarriers are physically located in different sites, the TAE may be muchlarger. Currently no such requirement exists.

SCell Activation and Deactivation

In LTE Release 10, Carrier Aggregation (CA) was introduced, and withthis introduction, the concept of SCells. That is additional resourceswhich could be configured or de-configured, and activated orde-activated on a per need basis. The activation or deactivationprocedure is described in detail in section 5.13 of 3GPP TS 36.213Medium Access Control (MAC) protocol specification.

Each SCell is configured with a Cell Index (CE), which may be denoted bySCelllndex. The SCelllndex is an identifier which is unique among allserving cells configured for this UE. The PCell will always have cellindex that is 0, and a SCell may have a cell index that is an integer of1 to 7, i.e. SCelllndex=1, . . . , 7.

One of the areas where MAC cell indexes are used is for activation anddeactivation of SCells. In LTE Release 10, the activation orde-activation of MAC cell indexes is defined in section 6.1.3.8 of 3GPPTS 36.213 Medium Access Control (MAC) protocol specification. Theactivation or de-activation of MAC cell indexes comprises a single octetin turn comprising seven C-fields and one R-field. Each C-fieldcorresponds to a specific SCelllndex. This indicates whether thespecific SCell is activated or deactivated. The UE will ignore allC-fields that are associated with cell indexes that are not configured.The activation or de-activation of MAC cell indexes always indicates theactivation status of all configured SCells. This means that if thenetwork node wants to activate one SCell, the network node has toinclude all configured SCells and set them to activated or deactivatedeven if their status has not changed.

Initial TAC and Subsequent TAC

A timing advance value, i.e. TA value, is used by the UE to offset theUL transmission timing relative a timing reference.

For random access, the UE may assume an initial TA value of zero. Thenetwork node measures the time misalignment of the desired UL timing onthis cell, and the actual UL timing of the preamble transmission. Thenetwork node then creates an initial TA command comprising informationwhich tells the UE how much to advance the UL transmission.

After the random access is successfully completed, the UE will initiateUL transmission on cell i at a time T_(i) before it receives the DLsubframe starting on cell i. The time T_(i) is deduced from the TA valuefor the cell i. When receiving these subsequent UL transmissions, thenetwork node also measures the time misalignment of the desired ULtiming for this cell and the actual UL timing from the UE on this cell.If measured time misalignment is exceeding a certain value, the networknode creates a TA command comprising a delta update, i.e. a timingadvance update, for the TA command which is sent to the UE.

In the current release, the initial TA value is an 11 bit long value andis sent in the random access response message. This TA value conveys tothe UE how much the UL transmission on a cell should be advanced inrelation to a timing reference. In LTE Release 10, this reference timingis the DL of the PCell. Subsequent TA values are updates of the currentTA value. The subsequent TA values may be carried in a 6 bit long valueand be sent in a MAC control element.

It should be noted that subsequent TA values may be delta updates of thecurrent TA value. Hence, an initial TA value is needed for subsequent TAdelta updates to be meaningful. This means that a random access isneeded for subsequent TA commands to be meaningful.

In carrier aggregation, the UE may change the cell in a TA group that isused as a timing reference for adjustments of the UL transmit timing.This means that the transmit timing of the new cell to be used as thetiming reference may be significantly different compared to that of theprevious cell that was used as a timing reference. This change may leadto substantial performance degradation at the network node.

This means that because a change in the timing reference serving cellfor a group of serving cells, i.e. TA group, may occur from one subframeto another, there may be an abrupt and significant change in thetransmit timing of uplink transmissions on the group of serving cells.This is because the transmit timing of uplink transmissions on the groupof serving cells is dependent upon the reference timing of the currenttiming reference serving cell. In other words, a large differencebetween the reference timing of the new timing reference serving celland the reference timing of the previous timing reference serving cellmay cause a sudden and relatively large change in the transmit timing ofthe uplink transmissions on the group of serving cells. This sudden andrelatively large change in the transmit timing may cause problems in thereception of the uplink transmission at the network node, since e.g. thereceiver in the network node may not be able to follow such a changefrom one subframe to another, and consequently lead to performancedegradation in the network node.

SUMMARY

It is an object of embodiments herein to prevent performance degradationin a network node.

According to a first aspect of embodiments herein, the object isachieved by a method in a user equipment for adjusting a transmit timingof uplink transmissions to a network node in a telecommunicationssystem. The user equipment is configurable with more than one aggregatedserving cells. The more than one aggregated serving cells are dividedinto one or more groups of serving cells based on a timing advance valueof each of the aggregated serving cells. The one or more groups ofserving cells each comprises a timing reference serving cell. Thereception timing of a downlink transmission from a timing referenceserving cell is used as a timing reference for the transmit timing ofuplink transmissions for the serving cells in the group of serving cellscomprising the timing reference serving cell, respectively. The userequipment determines a change to a second timing reference serving cellin a group of serving cells, which second timing reference serving cellis different from a first timing reference serving cell currently beingused as the timing reference serving cell for the group of servingcells. The user equipment then applies an incremental adjustment of thetransmit timing of uplink transmissions for the serving cells in thegroup of serving cells with respect to a timing reference based on thereception timing of a downlink transmission from the second timingreference serving cell in the user equipment.

According to a fourth aspect of embodiments herein, the object isachieved by a user equipment for adjusting a transmit timing of uplinktransmissions to a network node in a telecommunications system. The userequipment is configurable with more than one aggregated serving cells.The more than one aggregated serving cells are divided into one or moregroups of serving cells based on a timing advance value of each of theaggregated serving cells. The one or more groups of serving cells eachcomprises a timing reference serving cell. The reception timing of adownlink transmission from a timing reference serving cell is used as atiming reference for the transmit timing of uplink transmissions for theserving cells in the group of serving cells comprising the timingreference serving cell, respectively. The user equipment comprises aprocessing circuitry configured to determine a change to a second timingreference serving cell in a group of serving cells, which second timingreference serving cell is different from a first timing referenceserving cell currently being used as the timing reference serving cellfor the group of serving cells. The processing circuitry is furtherconfigured to apply an incremental adjustment of the transmit timing ofuplink transmissions for the serving cells in the group of serving cellswith respect to a timing reference based on the reception timing of adownlink transmission from the second timing reference serving cell inthe user equipment.

According to a third aspect of embodiments herein, the object isachieved by a method in a network node for determining information foradjusting a transmit timing of uplink transmissions of a user equipmentin a telecommunications system. The user equipment is configurable withmore than one aggregated serving cells. The more than one aggregatedserving cells are divided into one or more groups of serving cells basedon a timing advance value of each of the aggregated serving cells. Theone or more groups of serving cells each comprises a timing referenceserving cell. The reception timing of a downlink transmission from atiming reference serving cell in the user equipment is used as a timingreference for the transmit timing of uplink transmissions to the networknode for the serving cells in the group of serving cells comprising thetiming reference serving cell, respectively. The network node selects anew timing reference serving cell for a group of serving cellscomprising the user equipment. The network node then determineadjustment information for an incremental adjustment of the transmittiming of uplink transmissions for the serving cells in the group ofserving cells with respect to a timing reference based on the receptiontiming of a downlink transmission from a second timing reference servingcell in the user equipment, which second timing reference serving cellis different from a first timing reference serving cell on which thetiming reference is currently based.

According to a second aspect of embodiments herein, the object isachieved by a network node for determining information for adjusting thetransmit timing of uplink transmissions of a user equipment in atelecommunications system. The user equipment is configurable with morethan one aggregated serving cells. The more than one aggregated servingcells are divided into one or more groups of serving cells based on atiming advance value of each of the aggregated serving cells. The one ormore groups of serving cells each comprises a timing reference servingcell. The reception timing of a downlink transmission from a timingreference serving cell in the user equipment is used as a timingreference for the transmit timing of uplink transmissions to the networknode for the serving cells in the group of serving cells comprising thetiming reference serving cell, respectively. The network node comprisesa processing circuitry configured to select a new timing referenceserving cell for a group of serving cells comprising the user equipment.The processing circuitry is further configured to determine adjustmentinformation for an incremental adjustment of the transmit timing ofuplink transmissions for the serving cells in the group of serving cellswith respect to a timing reference based on the reception timing of adownlink transmission from a second timing reference serving cell in theuser equipment, which second timing reference serving cell is differentfrom a first timing reference serving cell on which the timing referenceis currently based.

By determining a change to a new timing reference serving cell, i.e. thesecond timing reference serving cell, and applying an incrementaladjustment of the transmit timing of uplink transmissions for theaffected cells based on this new timing reference serving cell asdescribed above, sudden and relatively large changes in the transmittiming of the uplink transmission is avoided.

Hence, by avoiding sudden and relatively large changes in the transmittiming, uplink transmission for the affected cells will be correctlyreceived in the network node and thus ensuring that the performance ofin the network node is not degraded.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the embodiments willbecome readily apparent to those skilled in the art by the followingdetailed description of exemplary embodiments thereof with reference tothe accompanying drawings, wherein:

FIG. 1 is a schematic block diagram of a LTE downlink physical resource,

FIG. 2 is a schematic overview depicting radio frames,

FIG. 3 is a schematic overview depicting a DL sub-frame,

FIG. 4 is a schematic overview depicting carrier aggregation,

FIG. 5 is a schematic overview depicting user equipments located atdifferent distances from a network node,

FIG. 6 is a schematic overview illustrating timing advance of uplinktransmissions from user equipments located at different distances from anetwork node,

FIG. 7 is a schematic block diagram illustrating embodiments in atelecommunications system,

FIG. 8 is a flowchart depicting embodiments of a method in a userequipment,

FIG. 9 is a flowchart depicting embodiments of a method in a networknode,

FIG. 10 is a signalling diagram illustrating exemplary timing advanceusing a timing reference serving cell,

FIG. 11 is a signalling diagram illustrating exemplary timing advanceusing another timing reference serving cell,

FIG. 12 is a schematic block diagram of embodiments of a network node,

FIG. 13 is a schematic block diagram of embodiments of a user equipment.

DETAILED DESCRIPTION

The figures are schematic and simplified for clarity, and they merelyshow details which are essential to the understanding of theembodiments, while other details have been left out. Throughout, thesame reference numerals are used for identical or corresponding parts orsteps.

As part of the developing the embodiments described herein, a problemwill first be identified and discussed.

In some scenarios, it has been noted that no mechanism exists whichdefines how a user equipment should adjust its transmit timing of uplinktransmissions for a group of serving cells, i.e. a TA group,autonomously when a change of the timing reference serving cell withinthe TA group has occurred. Thus, the user equipment is left with noother choice than to adjust its transmit timing of uplink transmissionsfor the TA group by following the reference timing of the new timingreference serving cell immediately after the change of the timingreference serving cell within the TA group has occurred.

In other words, since the downlink frame timing of the new timingreference serving cell in the TA group may be different than that of thedownlink frame timing of the previous timing reference serving cell inthe TA group, the straight forward solution is that the user equipmentadjusts its uplink transmit timing immediately according to the downlinktiming of the new timing reference serving cell.

For example, the difference in the transmit timing, e.g. the downlinkframe timing, between the new timing reference serving cell and theprevious timing reference serving cell may be as large as around 1.3 μs.However, for non co-located serving cells, i.e. serving cells which arelocated in different geographical sites, the difference in the downlinkframe timing may even be larger.

Furthermore, the new timing reference serving cell may also have beenrecently activated and its transmit timing may not have fullystabilized. Hence, an overall difference in the transmit timing ofdifferent serving cells may momentarily become very large.

This may lead to substantial performance degradation at the receiver inthe network node when there is a large difference between the referencetiming of the new timing reference serving cell in a TA group comparedto the previous timing reference serving cell, e.g. in the order of fewμs. The performance degradation may, for example, be degradation in thedemodulation of the signals transmitted by the user equipment.

It should also be noted that in some scenarios, there may also be anadditional requirement on a user equipment to autonomously adjust thetransmit timing of uplink transmission in a TA group in response to adrift in the transmit timing of the network node. The drift in thetransmit timing of the network node may, for example, be caused by asudden change in propagation conditions or variations in radioconditions, a drift due to imperfection in clocks, maintenanceactivities, or deliberate attempts by the network node to change thetiming, etc.

Hence, since conventional user equipments are required to follow thechange in the frame transmit timing of the timing reference servingcell, and correspondingly adjust the transmit timing of uplinktransmission on the serving cells in the TA group for each transmission,the aggregated time misalignment between the reference timing of the newtiming reference serving cell and the reference timing of the previoustiming reference serving cell may momentarily become significantly largefor this reason as well. This will further add to the performancedegradation at the network node.

Therefore, under such circumstances, a need has been identified todefine a mechanism which ensures that the user equipment does notperform any abrupt significant changes in the transmit timing of uplinktransmissions for a TA group.

Therefore some of the exemplary embodiments presented herein aredirected towards ways which prevents an abrupt change in a userequipments uplink transmit timing when the timing reference servingcell, i.e. the serving cell related to the timing reference, is changed.Instead, the user equipment changes its uplink timing gradually with acertain rate. This rate may also be referred to as a slew rate.

This change in the uplink transmit timing may imply an increase or adecrease in the uplink transmit timing. Therefore, the change of theuplink timing with a certain slew rate may be performed by the userequipment in either direction.

In other words, according to some of the exemplary embodiments presentedherein, when a serving cell in a TA group used by the user equipment forthe downlink timing reference (TR), i.e. a timing reference servingcell, is changed, the user equipment adjusts or changes its transmittiming for uplink transmissions for the TA group gradually, that is,applies incremental adjustments of the transmit timing.

In some embodiments, this gradual timing adjustment of the transmittiming of uplink transmissions for the TA group by the user equipmentmay be governed by a set of rules, by a set of network configurableparameters, or by a combination thereof. In some embodiments, the use ofrules for the gradual timing adjustment may also depend upon one or moreconditions, such as, e.g. signal quality of the timing reference servingcell, type of carrier aggregation, downlink timing difference betweenthe new timing reference serving cell and old timing reference servingcells used for the timing reference, etc.

According to some embodiments, examples of the gradual timing adjustmentmay be summarized as being part of the following main principles: timingadjustment triggering based on pre-defined rules, timing adjustmenttriggering based on explicit request from network node, or timingadjustment triggering based on combination of explicit request andpre-defined rules. This is described in more detail by the embodimentsshown and described in reference to the FIGS. 14-15 below.

FIG. 7 depicts a telecommunications system 100 in which embodimentsherein may be implemented. The cellular communications system 100 is awireless communication network such as an LTE, WCDMA, GSM network, any3GPP cellular network, or any cellular network or system.

The telecommunications system 100 comprises a base station, which is anetwork node and is therefore referred to herein as the network node110. The network node 110 may in this example e.g. be an eNB, eNodeB, ora Home Node B, a Home eNode B, femto Base Station (BS), pico BS or anyother network unit capable to serve a user equipment or a machine typecommunication device, such as e.g. the user equipment 121.

The user equipment 121 is configured to communicate within thetelecommunications system 102 via the network node 110 over a radio link130 when served by the network node 110. The user equipment 121 may, forexample, be a mobile terminal or a wireless terminal, a mobile phone, acomputer such as for example a laptop, a Personal Digital Assistant(PDA) or a tablet computer, sometimes referred to as a surf plate, withwireless capability, a device equipped with a wireless interface, suchas a printer or a file storage device or any other radio network unitcapable of communicating over a radio link in a telecommunicationssystem.

Embodiments of a method in the user equipment 121 will now be describedwith reference to the flowchart depicted in FIG. 8. FIG. 8 is anillustrating example of a flow chart for a method in the user equipment121 for adjusting the transmit timing of uplink transmissions of theuser equipment 121 in the telecommunications system 100. The userequipment 121 is configurable with more than one aggregated servingcells, i.e. the user equipment 121 may be configured with more than oneaggregated serving cells. The more than one aggregated serving cells aredivided into one or more groups of serving cells, i.e. TA groups, basedon the TA value of each of the aggregated serving cells. The one or moregroups of serving cells, i.e. TA groups, each comprises a timingreference serving cell. As will be described in reference to FIGS. 10-11below, the reception timing of a downlink transmission from a timingreference serving cell is used as a timing reference for a transmittiming of uplink transmissions for the serving cells in the group ofserving cells, i.e. the TA group, comprising the timing referenceserving cell, respectively.

FIG. 8 is an illustrating example of detailed exemplary actions oroperations which may be taken by a user equipment 121. It should beappreciated that the flowchart diagram is provided merely as an exampleand that the user equipment 121 may be configured to perform any of theexemplary actions or operations provided herein. It should beappreciated that the actions or operations illustrated below are merelyexamples, thus it is not necessary for all the actions or operations tobe performed. It should also be appreciated that the actions oroperations may be performed in any combination. Furthermore, theflowchart in FIG. 8 comprises the following actions, and may beimplemented for any of the above and below mentioned embodiments or inany combination with those.

Action 801

In some embodiments, the user equipment 121 may receive adjustmentinformation from the network node 110. This may be performed in caseswhere it would be beneficial to have the network node 110 determine theadjustment of the transmit timing of uplink transmissions of the userequipment 121, e.g. as described below with reference to the embodimentsof a network node 110 in FIG. 9.

In other words, the user equipment 121 may receive at least oneparameter, e.g. from the network node 110, to be utilized in anincremental adjustment described in Action 803. This may imply that theuser equipment 121 receives an adjustment request or an adjustmentnotification from the network node 110.

The adjustment information, e.g. the at least one parameter, may be e.g.a maximum magnitude in an uplink timing change per increment, a minimumaggregate uplink timing adjustment rate, or a maximum aggregate uplinktiming adjustment rate. The at least one parameter may be comprised inthe adjustment request or the adjustment notification. This means thatthe user equipment 121 may receive at least one parameter associatedwith the incremental adjustment. As described in Action 803, the userequipment 121 may utilize the at least one parameter in the applying ofthe incremental adjustment.

Action 802

In this action, the user equipment 121 determines a change to a secondtiming reference serving cell in a group of serving cells. The secondtiming reference serving cell is different from a first timing referenceserving cell currently being used as the timing reference serving cellfor the group of serving cells. The group of serving cells is the TAgroup of the user equipment 121. In other words, the user equipment 121determines the presence of a new timing reference cell, i.e. the secondtiming reference serving cell.

In some embodiments, the user equipment 121 determine a change to thenew timing reference serving cell by being informed by the network, e.g.the network node 110 or eNB, regarding the change of the timingreference serving cell. This information may be acquired by the userequipment 121 explicitly, e.g. by receiving an adjustment request or anadjustment notification from the network node 110 as described in theprevious Action 801. This may be referred to as timing adjustmenttriggering based on an explicit request from network.

In some embodiments, the user equipment 121 determine a change to a newtiming reference serving cell by being informed implicitly regarding thechange of the timing reference serving cell, e.g. by receiving atriggering event. The triggering event may be based on at least onetriggering rule in the user equipment 121. For example, the at least onetriggering rule may be based on a timing threshold. Thus, the triggeringevent may be provided in the user equipment 121 when an adjustment inuplink timing in response to the new timing reference serving cell wouldcause a change that is greater to or equal to the timing threshold. Thismay also be referred to as timing adjustment triggering based onpre-defined rules.

This implicit mechanism, i.e. triggering rule, may e.g. be that aserving cell in TA group with certain characteristics may be consideredas the timing reference serving cell for the TA group, or be determinedby a change in the index or sequence numbers assigned to the servingcells in the TA group. In the latter, a cell with the lowest or thehighest index in a TA group may, for example, be defined as the timingreference serving cell for the TA group. Such changes may also beexplicitly made to the user equipment 121 by the network node 110.

Action 803

In this action, the user equipment 121 applies an incremental adjustmentof the transmit timing of uplink transmissions for the serving cells inthe group of serving cells. This is performed with respect to a timingreference based on the reception timing of a downlink transmission fromthe second timing reference serving cell in the user equipment 121. Inother words, the user equipment 121 applies an incremental adjustment ofthe uplink transmission timing with respect to the new timing referencecell, i.e. the second timing reference serving cell.

This incremental or gradual adjustment to a new uplink transmit timingupon a change of the timing reference serving cell will give a smoothtransition between the transmit timing of uplink transmissions of theprevious timing reference serving cell, i.e. the first timing referenceserving cell, and the transmit timing of uplink transmissions of the newtiming reference serving cell, i.e. the second timing reference servingcell.

It should also be noted that applying this incremental adjustment maycomprise applying an incremental advance or retreat of the uplinktransmission timing. Also, applying this incremental adjustment maycomprise analyzing a total adjustment to be made with respect to atiming threshold, and determining a number of increments of theincremental adjustment based on this analysis. Further, applying thisincremental adjustment may comprise choosing the new timing referencecell as an activated secondary cell with a lowest index value, andapplying the incremental adjustment with respect to the activatedsecondary cell with the lowest index value.

According to some embodiments, the incremental adjustment, i.e. transmittiming adjustment, may be based on pre-defined rules or applicationrules.

The gradual change in the transmit timing of uplink transmissions, i.e.uplink timing, upon change of the timing reference serving cell may beperformed by the user equipment 121 over a certain period of time. Thismeans that it is performed with a certain rate or with a certain slewrate. The user equipment 121 may thus follow pre-defined increment stepsover the certain period of time, i.e. a certain pre-defined timeinterval or slope. The maximum adjustment step may also be pre-defined.

More specifically, the pre-defined rules governing the adjustments ofthe transmit timing of uplink transmissions, i.e. the uplink timingadjustments, made by the user equipment 121 in response to the change ofthe serving cell in the TA group used as the timing reference servingcell may comprise:

-   -   T1—a maximum amount of the magnitude of the uplink timing change        in one adjustment step;    -   T2—a minimum aggregate uplink timing adjustment rate over a        certain period of time, or    -   T3—a maximum aggregate uplink timing adjustment rate over a        certain period of time.

In some embodiments, T1 may e.g. be 100 ns, T2 may e.g. be 300 ns persecond, and T3 may e.g. be 1 μs per 200 ms. T1-T3 are parametersdetermining maximum or aggregated minimum or maximum adjustment stepsover their respective time periods.

It should be noted that the magnitude of the incremental adjustment maybe less than the magnitude of the difference between the receptiontimings of downlink reception transmissions of the previous timingreference serving cell and the new timing reference serving cell, whenthe magnitude of the difference is above a threshold.

Furthermore the above stated parameters of the predefined rules orapplication rules, i.e. T1-T3, may also depend upon one or more of thefollowing factors:

-   -   The bandwidth of the transmitted signals. For example, the        downlink cell transmission bandwidth and/or the uplink cell        transmission bandwidth. Another example, is if a previous and        new timing reference serving cell belongs to different frequency        bands, or if a previous and new timing reference serving cells        are separated in the frequency domain by a predetermined margin,        for example, non-contiguous carriers in the same band;    -   The type of carrier aggregation (CA) scheme. For example,        intra-band contiguous CA, intra-band non-contiguous CA,        inter-band CA, etc.;    -   A user equipment activity factor. For example, whether the user        equipment 121 is in a Discontinuous Reception (DRX) state or a        non-Discontinuous Reception state, or whether the user equipment        121 is in a Discontinuous Transmission (DTX) state or a        non-Discontinuous Transmission state. If the user equipment 121        is in a DRX or in a DTX state, the user equipment activity        factor may also be e.g. the DRX or DTX length, etc.;    -   The type of physical channel. For example, an uplink data        channel, such as, e.g. PUSCH, or an uplink control channel, such        as, e.g. PUCCH, etc. Another example is if the user equipment        121 transmits a particular signal using a particular channel,        such as, e.g. PUSCH, sounding reference signal, SRS, etc.;    -   Whether or not the serving cells involved in CA or CoMP are        co-located or not;    -   A radio characteristic. For example, a user speed such as a user        equipment speed above a predetermined threshold, a radio        environment such as with a larger delay spread, a deployment        scenario such as urban, etc. Another example is when the        downlink signal quality of the new timing reference serving cell        is poor, i.e. below threshold. This may be e.g. when one or more        of SINR, RSRP, RSRQ, CSI, etc., are below their respective        thresholds. A further example is when the user equipment 121 has        not performed any measurement or any specific measurement, e.g.        RSRP, on the new timing reference serving cell over the last T4        seconds. T4 may e.g. be 5 seconds. Yet a further example is when        radio characteristics lead to a large drift in the downlink        timing of new timing reference serving cell, e.g. when the delay        spread is above a threshold, such as, e.g. 2 μs or more.

This means that the incremental adjustment may be applied based on atleast one application rule, wherein the at least one application rulemay provide for an adjustment amount for each incremental step of theadjustment.

This also means that the at least one application rule may be associatedwith, e.g. a bandwidth of transmitted signals, a type of carrieraggregation scheme, a user equipment activity factor, a type of physicalchannel, whether or not cells are co-located or not, or radiocharacteristics.

The at least one application rule may also be provided by the networknode 110, e.g. in the receiving of adjustment information from thenetwork node 110 as described in Action 801.

According to some embodiments, the gradual change of the uplinktransmission timing, that is, the pre-defined rules that may be relatedto the uplink timing adjustments in response to change of the servingcell in a TA group, may e.g. be applied by the user equipment 121 if oneor more of the following conditions are met.

One condition may be that the difference in the magnitude of thedownlink reception timing between the new timing reference serving celland the previous timing reference serving cell in a TA group is largerthan a certain threshold D1. The threshold D1 may e.g. be more than 1μs. This means that if the difference in the downlink reception timingof the new timing reference serving cell and the previous timingreference serving cell is smaller than the value of the threshold D1,the uplink transmission timing may be changed in a conventional way bysimply following the downlink timing of the new timing reference servingcell.

This may be performed even for all the transmissions in the uplink. Thismeans that the user equipment 121 may change the uplink transmissiontiming abruptly even in the first transmission to the network node 110.The threshold value D1 may be pre-defined in the user equipment 121, orbe signalled by the network node 110 to the user equipment 121.

Another condition may be that a specific type of carrier aggregation isused. For example, that an inter-band carrier aggregation is used. Afurther condition may be that the new timing reference serving cell andthe previous timing reference serving cell belong to different frequencybands or are separated in the frequency domain by a certain differenceor margin, e.g. non-contiguous carriers in the same band). A furthercondition may also be that the particular radio characteristics lead toa large drift in downlink timing of the new timing reference servingcell, such as, e.g. when the delay spread is above a certain threshold,e.g. 2 μs or more.

A further condition may also be that the speed of the user equipment 121is above a speed threshold, such as, e.g. over 90 km/hr. This is becausea large fading dip, which may occur during high speeds of the userequipment 121, may lead to sudden changes in timing. A further conditionmay also be that the user equipment 121 transmits a particular signal ortransmits using a particular channel, such as, e.g. PUSCH, SRS, etc.

Yet a further condition may be that the downlink signal quality of thenew timing reference serving cell is poor, i.e. below certain threshold.For example, when one or more of SINR, RSRP, RSRQ, CSI, etc., is/arebelow respective thresholds. This is because the timing of the newtiming reference serving cell may not be fully reliable, and therefore agradual change in the uplink timing may be desirable. Yet a furthercondition may also be that the user equipment 121 has not performed anymeasurement, or any specific measurement, such as, e.g. RSRP, on the newtiming reference serving cell over a particular time period. Theparticular time period may e.g. be the last T4 seconds, which may bee.g. 5 seconds.

Embodiments of a method in the network node 110 will now be describedwith reference to the flowchart depicted in FIG. 9. FIG. 9 is anillustrating example of a flow chart for a method in the network node110 for determining information for adjusting the transmit timing ofuplink transmissions of the user equipment 121 in the telecommunicationssystem 100. The user equipment 121 is configurable with more than oneaggregated serving cells. The more than one aggregated serving cells aredivided into one or more groups of serving cells, i.e. TA groups, basedon the TA value of each of the aggregated serving cells. The one or moregroups of serving cells, i.e. TA groups, each comprises a timingreference serving cell. As described in reference to FIGS. 10-11 below,the reception timing of a downlink transmission from a timing referenceserving cell is used as a timing reference for the transmit timing ofuplink transmissions for the serving cells in the group of servingcells, i.e. TA group, comprising the timing reference serving cell,respectively.

FIG. 9 is an illustrating example of detailed exemplary actions oroperations which may be taken by a network node 110. It should beappreciated that the flowchart diagram is provided merely as an exampleand that the network node 110 may be configured to perform any of theexemplary actions or operations provided herein. It should beappreciated that the actions or operations illustrated below are merelyexamples, thus it is not necessary for all the actions or operations tobe performed. It should also be appreciated that the actions oroperations may be performed in any combination. Furthermore, theflowchart in FIG. 9 comprises the following actions, and may beimplemented for any of the above and below mentioned embodiments or inany combination with those.

Action 901

In some embodiments, the network node 110 may select a second timingreference serving cell. This means that the network node 110 may selectthe second timing reference serving cell as the timing reference servingcell for a group of serving cells, i.e. a TA group, comprised in theuser equipment 121.

Action 902

In this action, the network node 110 determines adjustment informationfor an incremental adjustment of the transmit timing of uplinktransmissions for the serving cells in the group of serving cells, i.e.the TA group, with respect to a timing reference based on the receptiontiming of a downlink transmission from a second timing reference servingcell in the user equipment 121. The second timing reference serving cellis different from a first timing reference serving cell on which thetiming reference is currently based.

According to some embodiments, the adjustment information may be arequest to apply an incremental adjustment of the uplink transmissiontiming or a notification that a new timing reference serving cell isbeing utilized. The incremental adjustment may be an advance or retreatof the uplink transmission timing. Also, the adjustment information maycomprise a selected new timing reference serving cell. In someembodiments, the selected new timing reference serving cell may be anactivated secondary cell with a lowest index value.

For example, according to some embodiments, the network node 110 mayselect a value of the threshold D1 as described above with reference toembodiments of the user equipment 121. The value of the threshold D1 maybe based on one or more criteria that are related to the capability ofthe receiver in the network node 110, i.e. the base station receivercapability. For example, if the receiver in the network node 110 is amore robust receiver, then the network node 110 may select the value ofthe threshold D1 such that the user equipment 121 is allowed to apply agradual change in the uplink transmission timing when the downlinktiming difference between the new timing reference serving cell and theprevious timing reference serving cell is larger. According to oneexample, this means that the value of the threshold D1 may e.g. be morethan 2 μs for the downlink timing difference between the new timingreference serving cell, i.e. the second timing reference serving cell,and the previous timing reference serving cell, i.e. the first timingreference serving cell, instead of e.g. more than 1 μs for a less robustreceiver in the network node 110.

If the value of the threshold D1 is pre-defined in the user equipment121, the network node 110 may still configure the user equipment 121when to use this pre-defined threshold D1.

As previously mentioned, according to some embodiments, the incrementaladjustment, i.e. the transmit timing adjustment, may be based on anexplicit request from the network node 110. According to someembodiments, this means that the network node 110 explicitly mayindicate whether the user equipment 121 should gradually change itsuplink transmission timing or not, when the timing reference servingcell in a TA group is changed.

The pre-defined rules described above with reference to embodiments ofthe user equipment 121 on how to change the uplink transmission timingmay still apply. However, the parameter values may be configurable. Forexample, the network node 110 may configure the user equipment 121 withone or more parameters, such as, parameters that are associated with thegradual change in the uplink transmission timing. This may e.g. be themaximum amount of the magnitude of the uplink timing change in oneadjustment step, the minimum aggregate uplink timing adjustment rate,the maximum aggregate uplink timing adjustment rate, etc. The parametersmay e.g. be the parameters T1-T3 described above with reference toembodiments of the user equipment 121.

The network node 110 may also select the parameters depending uponcertain radio characteristics, such as, e.g. cell bandwidth (BW), radioconditions, activity level, carrier aggregation type, robustness of thereceiver used at the network node 110, etc. If the receiver at thenetwork node 110 is a more robust receiver, then the network node 110may receive and process received uplink signals with a larger change inuplink transmission timing over a shorter period of time. In summary,according to some embodiments, the parameters as described for thepre-defined rules, application rules and/or conditions above withreference to embodiments of the user equipment 121 may be configured bythe network node 110. This advantageously provides for more flexibilityin the telecommunications system 100.

According to some embodiments, the incremental adjustment, i.e. transmittiming adjustment, may be based on a combination of the explicit requestfrom the network node 110 and the pre-defined rules as described abovewith reference to embodiments of the user equipment 121. According tosome embodiments, this means that the rules and values of the associatedparameters governing the gradual change in the uplink transmissiontiming may be pre-defined, as described above with reference toembodiments of the user equipment 121.

However, the network node 110 may also explicitly indicate whether theuser equipment 121 should apply the rules and values related to thegradual change in the uplink transmission timing, when the timingreference serving cell in a TA group has changed. In this case, the userequipment 121 may change the uplink transmission timing gradually onlyif the network node 110 indicates this explicitly. The network node 110may also indicate the condition under which the user equipment 121should apply the pre-defined rules. For example, the network node 110may indicate that the user equipment 121 should apply the rules only ifits speed is above a particular threshold.

Action 903

According to some embodiments, the network node 110 may, in thisoptional action, transmit the adjustment information to the userequipment 121. The transmitting may be performed based on triggeringrules. The triggering rule(s) may be based on a timing threshold.

If the user equipment 121 changes its uplink transmission timing toofast when the timing reference serving cell in a TA group is changed,the receiver at the network node 110 may not be able to handle thereception of the signals from the user equipment 121. This will degradethe uplink performance of the network node 110 and e.g. result in a lossin uplink system throughput.

The embodiments described herein avoid these problems relating to thechange in the timing reference serving cells with different downlinkreception timing. The behaviour of the user equipment 121 with respectto the rate of the change of the uplink transmission timing is defined.This ensures consistency in the behaviour of the user equipment 121.

FIG. 10 depicts a signalling diagram between the network node 110 andthe user equipment 121 illustrating an exemplary timing advance using atiming reference serving cell.

As previously described, with the introduction of TA grouping in the LTERelease 11, it is possible to group the serving cells of a userequipments 121 into TA groups depending on the TA values of the servingcells. Thus, the user equipment 121 supports more than one aggregatedserving cells. The more than one aggregated serving cells are dividedinto one or more groups of serving cells, i.e. TA group(s), based on theTA value of each of the aggregated serving cells.

Each TA group may have an associated TA timer. The TA timer may controlthe validity of a defined TA value. This means that as long as the TAtimer is running, the defined TA value is considered valid. If thedefined TA value is valid, the user equipment 121 is consideredsynchronized for uplink transmissions on the serving cells associatedwith the defined TA value, i.e. the serving cells belonging to the TAgroup. The TA timer will be restarted upon reception of a TA commandwhich updates the TA value. If no TA command is received for a certainperiod of time, the TA timer may expire. However, the TA timer may alsobe set to infinity, in which case the TA timer will not expire.

In each TA group, there will be one serving cell defined as the timingreference serving cell. This means that the one or more groups ofserving cells, supported by the user equipment 121, each comprises atiming reference serving cell. The uplink transmission timing on theserving cells in a TA group will be in relation to the downlinkreception timing on the timing reference serving cell. This means thatthe reception timing of a downlink transmission on a timing referenceserving cell is used as a timing reference for the transmit timing ofuplink transmissions on the cells in the group of serving cellscomprising the timing reference serving cell, respectively.

The uplink transmission timing in a TA group may be the downlinkreception timing of the timing reference serving cell in that TA groupminus the TA value for this TA group. This means that the transmittiming of uplink transmissions for the serving cells in the group ofserving cells comprising the timing reference serving cell is determinedas the reception timing of a downlink transmission from the timingreference serving cell minus the TA value of the group of serving cellscomprising the timing reference serving cell.

The signalling diagram in FIG. 10 may comprise the following actions,and may be implemented for any of the below mentioned embodiments or inany combination with those. Note that an overview of the signallingdiagram is illustrated in FIG. 10, and that all the actions performedmay not be shown in order to simplify.

Action 1001

In this action, the user equipment 121 transmits an uplink signal on aserving cell A and a serving cell B. The user equipment 121 isconfigured with the two serving cells A and B. The serving cells A and Bare placed in the same TA group, wherein the serving cell A is thetiming reference serving cell for this TA group. Hence, the servingcells A and B share the same timing reference and TA value. In otherwords, the timing reference for the serving cells A and B is based onthe reception timing of downlink transmissions on the timing referenceserving cell of the TA group to which the serving cells A and B belongs,i.e. the reception timing of downlink transmissions on the serving cellA. This means that the TA value for the serving cells A and B is thedefined TA value associated with the TA group to which the serving cellsA and B belong.

Therefore, the user equipment 121 will have the same uplink transmissiontiming for these two cells. This means that the transmit timing of theuplink transmissions on the serving cells A and B will be the same, asindicated by the fully drawn and dashed arrows in the signalling diagramin FIG. 10.

Actions 1002-1003

It should be noted that exemplary requirements for the downlink timealignment of two serving cells may be 130 ns for serving cells in thesame frequency band, 260 ns for non-contiguous serving cells in the samefrequency band, and 1.3 μs for serving cells in difference frequencybands. This illustrates that the transmit timing of the downlinktransmissions may not be assumed to be the identical for the servingcells A and B, but that there may be some time difference.

Thus, in these actions and as an example, the network node 110 firsttransmit a downlink signal on the serving cell A and later transmit adownlink signal on the serving cell B, as indicated by the fully drawnand dashed arrows in the signalling diagram in FIG. 10.

Actions 1004-1005

In these actions, the user equipment 121 receives the downlink signal onthe serving cell A and the downlink signal on the serving cell B timeshifted. The user equipment 121 then applies the TA value to thedownlink reception timing of the timing reference serving cell, i.e. theserving cell A, in order to calculate the transmit timing for uplinktransmissions on the serving cells in the TA group, i.e. the servingcells A and B. The user equipment 121 may then transmit uplink signalson both the serving cell A and the serving cell B at that calculatedtime.

FIG. 11 depicts a signalling diagram between the network node 110 andthe user equipment 121 illustrating an exemplary timing advance usinganother timing reference serving cell than in FIG. 10. The signallingdiagram in FIG. 11 may comprise the following actions, and may beimplemented for any of the below mentioned embodiments or in anycombination with those. Note that an overview of the signalling diagramis illustrated in FIG. 11, and that all the steps performed may not beshown in order to simplify.

Action 1101

In this action, the user equipment 121 transmits an uplink signal on aserving cell A and a serving cell B. The user equipment 121 isconfigured with the two serving cells A and B. The serving cells A and Bare placed in the same TA group, wherein the serving cell B is thetiming reference serving cell for this TA group. Hence, the servingcells A and B share the same timing reference and TA value. In otherwords, the timing reference for the serving cells A and B is based onthe reception timing of downlink transmissions on the timing referenceserving cell of the TA group to which the serving cells A and B belongs,i.e. the reception timing of downlink transmissions on the serving cellB. This means that the TA value for the serving cells A and B is thedefined TA value associated with the TA group to which the serving cellsA and B belong.

Therefore, the user equipment 121 will have the same uplink transmissiontiming for these two cells. This means that the transmit timing of theuplink transmissions on the serving cells A and B will be the same, asindicated by the fully drawn and dashed arrows in the signalling diagramin FIG. 11.

Actions 1102-1103

In these actions and as an example, the network node 110 may firsttransmit a downlink signal on the serving cell A and later transmit adownlink signal on the serving cell B, as indicated by the fully drawnand dashed arrows in the signalling diagram in FIG. 11.

Actions 1104-1105

In these actions, the user equipment 121 receives the downlink signal onthe serving cell A and the downlink signal on the serving cell B timeshifted. The user equipment 121 then applies the TA value to thedownlink reception timing of the timing reference serving cell, i.e. theserving cell B, in order to calculate the transmit timing for uplinktransmissions on the serving cells in the TA group, i.e. the servingcells A and B. The user equipment 121 may then transmit uplink signalson both the serving cell A and the serving cell B at that calculatedtime.

It is currently not determined in any standard how to select the timingreference serving cell in a TA group, i.e. how to select the servingcell which should act as the timing reference serving cell in a TAgroup. According some examples, the selection of the timing referenceserving cell may change from one subframe to another. The change of thetiming reference serving cell for a user equipment 121 may occur, forexample, by selecting a new timing reference serving cell or in that theserving cell acting as the timing reference serving cell is deactivated.According to other examples, the change of the timing reference servingcell for a user equipment 121 may occur in that the current timingreference serving cell is moved to another TA group, or in that the cellindexes of the serving cells configured for the user equipment 121 ischanged, etc. Because the transmit timing of uplink transmission on thecells in a TA group is in relation to the timing reference serving cellof that TA group, changing the serving cell acting as the timingreference serving cell will also mean that the transmit timing of uplinktransmissions is changed.

The uplink transmission timing is, as described, depending on thedownlink transmission timing of the timing reference serving cell. Thismeans that the transmit timing of uplink transmissions on the servingcells in a TA group depends on the reception timing of downlinktransmissions on the timing reference serving cell, and may be seen bystudying the transmit timing of the uplink transmissions in the FIGS.10-11.

In FIG. 10, the user equipment 121 is transmitting in uplink on theserving cells A and B earlier than the user equipment 121 in FIG. 11. Itmay thus be readily seen that changing the timing reference serving cellfor the TA group from being the serving cell A to being the serving cellB, or vice versa, will cause the user equipment 121 to advance, orretreat, the transmit timing of uplink transmission on the serving cellsin the TA group, respectively.

The example embodiments presented herein may be utilized in a radionetwork, which may further comprise network nodes, such as, a basestation 110, as illustrated in FIG. 12. The radio network may alsocomprise a user equipment 121, as illustrated in 13. It should beappreciated that the examples provided in FIGS. 12 and 13 are shownmerely as non-limiting examples. According to the example embodiments,the network node 110 and user equipment 121 may be any other node asdescribed in the examples provided in the above sections.

As shown in FIG. 12, the example network node 110 may compriseprocessing circuitry 1203, a memory 1202, radio circuitry 1201, and atleast one antenna. The processing circuitry 1203 may comprise RFcircuitry and baseband processing circuitry (not shown). In particularembodiments, some or all of the functionality described above as beingprovided by a mobile base station, a base station controller, a relaynode, a NodeB, an enhanced NodeB, positioning node, and/or any othertype of mobile communications node may be provided by the processingcircuitry 1203 executing instructions stored on a computer-readablemedium, such as the memory 1202 shown in FIG. 12. Alternativeembodiments of the network node 110 may comprise additional componentsresponsible for providing additional functionality, comprising any ofthe functionality identified above and/or any functionality necessary tosupport the solution described above. In other example embodiments, anetwork node may be not equipped with a radio interface or radiocircuitry 1201.

It should also be appreciated that the processing circuitry, or anyother hardware and/or software unit configured to execute operationsand/or commands, of the network node 110 illustrated in FIG. 12 may beconfigured to configure to provide assistance, information and/or acommand for a gradual UL timing adjustment in the presence of a servingcell TR change.

An example of a user equipment 121 is provided in FIG. 13. The exampleuser equipment 121 may comprise processing circuitry 1302, a memory1303, radio circuitry 1301, and at least one antenna. The radiocircuitry 1301 may comprise RF circuitry and baseband processingcircuitry (not shown). In particular embodiments, some or all of thefunctionality described above as being provided by mobile communicationdevices or other forms of wireless device may be provided by theprocessing circuitry 1302 executing instructions stored on acomputer-readable medium, such as the memory 1303 shown in FIG. 13.Alternative embodiments of the user equipment 121 may compriseadditional components responsible for providing additionalfunctionality, comprising any of the functionality identified aboveand/or any functionality necessary to support the solution describedabove.

It should be appreciated that the processing circuitry, or any otherhardware and/or software unit configured to execute operations and/orcommands, of the user equipment 121 may be configured to determine achange to a new timing reference serving cell. The user equipment may befurther configured to provide a gradual UL timing adjustment in thepresence of a timing reference (TR) serving cell change.

To perform the method actions for determining information for adjustingthe transmit timing of uplink transmissions of a user equipment 121, thenetwork node 110 comprises the following arrangement depicted in FIG.12. FIG. 12 shows a schematic block diagram of embodiments of thenetwork node 110.

The user equipment 121 is configurable with more than one aggregatedserving cells. The more than one aggregated serving cells are dividedinto one or more groups of serving cells based on a timing advance valueof each of the aggregated serving cells. The one or more groups ofserving cells each comprises a timing reference serving cell. Thereception timing of a downlink transmission from a timing referenceserving cell in the user equipment is used as a timing reference for thetransmit timing of uplink transmissions to the network node for theserving cells in the group of serving cells comprising the timingreference serving cell, respectively.

The network node 110 comprises a processing circuitry 1203 configured todetermine adjustment information for an incremental adjustment of thetransmit timing of uplink transmissions for the serving cells in thegroup of serving cells with respect to a timing reference based on thereception timing of a downlink transmission from a second timingreference serving cell in the user equipment 121, which second timingreference serving cell is different from a first timing referenceserving cell on which the timing reference is currently based.

The processing circuitry 1203 may further be configured to select thesecond timing reference serving cell as the timing reference servingcell for the group of serving cells comprised in the user equipment 121.

The network node 110 may comprise a radio circuitry 1201. The radiocircuitry 1201 may be configured to transmit the adjustment informationto the user equipment 121. The adjustment information may be a requestto apply an incremental adjustment of uplink transmission timing or anotification that a new timing reference serving cell is being utilized.

Also, the radio circuitry 1201 may further be configured to transmit theadjustment information based on triggering rules. The at least onetriggering rule may be based on a timing threshold. The incrementaladjustment may be an advance or retreat of the uplink transmissiontiming.

According to some embodiments, the adjustment information may comprise aselected new timing reference serving cell. The selected new timingreference serving cell may, e.g. be an activated secondary cell with alowest index value.

To perform the method actions for adjusting a transmit timing of uplinktransmissions to a network node 110, the user equipment 121 comprisesthe following arrangement depicted in FIG. 13. FIG. 13 shows a schematicblock diagram of embodiments of the user equipment 121.

The user equipment 121 is configurable with more than one aggregatedserving cells. The more than one aggregated serving cells are dividedinto one or more groups of serving cells based on a timing advance valueof each of the aggregated serving cells. The one or more groups ofserving cells each comprises a timing reference serving cell. Thereception timing of a downlink transmission from a timing referenceserving cell is used as a timing reference for the transmit timing ofuplink transmissions for the serving cells in the group of serving cellscomprising the timing reference serving cell, respectively.

The user equipment 121 comprises a processing circuitry 1302 configuredto determine a change to a second timing reference serving cell in agroup of serving cells. The second timing reference serving cell isdifferent from a first timing reference serving cell currently beingused as the timing reference serving cell for the group of servingcells. The processing circuitry 1302 is further configured to apply anincremental adjustment of the transmit timing of uplink transmissionsfor the serving cells in the group of serving cells with respect to atiming reference based on the reception timing of a downlinktransmission from the second timing reference serving cell in the userequipment (121).

The processing circuitry 1302 may further be configured to receive anadjustment request or an adjustment notification from the network node110. Also, the processing circuitry 1302 may further be configured toreceive a triggering event based on at least one triggering rule. The atleast one triggering rule may be based on a timing threshold, andwherein the triggering event is provided when an adjustment in uplinktransmission timing in response to the new timing reference serving cellwould cause a change that is greater to or equal to the timingthreshold. Further, the processing circuitry 1302 may further beconfigured to apply an incremental advance or retreat of the uplinktransmission timing.

Also, the processing circuitry 1302 may further be configured to applythe incremental adjustment based on at least one application rule. Theat least one application rule may provide an adjustment amount for eachincremental step of the adjustment. The at least one application rulemay, for example, be associated with a bandwidth of transmitted signals,a type of carrier aggregation scheme, a user equipment activity factor,a type of physical channel, whether or not cells are co-located or not,radio characteristics, etc. The application rules may be provided by thenetwork node 110.

According to some embodiments, the processing circuitry 1302 may furtherbe configured to analyze a total adjustment to be made with respect to atiming threshold and the processing circuitry 1302 may also beconfigured to determine a number of increments of the incrementaladjustment based on the analysis. According to some embodiments, theprocessing circuitry 1302 may further be configured to choose the newtiming reference cell as an activated secondary cell with a lowest indexvalue and applying the incremental adjustment with respect to theactivated secondary cell with the lowest index value.

The user equipment 121 may further comprise radio circuitry 1301configured to receive at least one parameter associated with theincremental adjustment. The processing circuitry 1302 may be configuredto utilize the at least one parameter in the application of theincremental adjustment. The at least one parameter may be a maximumamount of magnitude in an uplink timing change per increment, a minimumaggregate uplink timing adjustment rate, and/or a maximum aggregateuplink timing adjustment rate.

The description of the example embodiments provided herein have beenpresented for purposes of illustration. The description is not intendedto be exhaustive or to limit example embodiments to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of various alternativesto the provided embodiments. The examples discussed herein were chosenand described in order to explain the principles and the nature ofvarious example embodiments and its practical application to enable oneskilled in the art to utilize the example embodiments in various mannersand with various modifications as are suited to the particular usecontemplated. The features of the embodiments described herein may becombined in all possible combinations of methods, apparatus, modules,systems, and computer program products. It should be appreciated thatthe example embodiments presented herein may be practiced in anycombination with each other.

It should be noted that the word “comprising” does not necessarilyexclude the presence of other elements or steps than those listed andthe words “a” or “an” preceding an element do not exclude the presenceof a plurality of such elements. It should further be noted that anyreference signs do not limit the scope of the claims, that the exampleembodiments may be implemented at least in part by means of bothhardware and software, and that several “means”, “units” or “devices”may be represented by the same item of hardware.

A “device” as the term is used herein, is to be broadly interpreted toinclude a radiotelephone having ability for Internet/intranet access,web browser, organizer, calendar, a camera (e.g., video and/or stillimage camera), a sound recorder (e.g., a microphone), and/or globalpositioning system (GPS) receiver; a personal communications system(PCS) terminal that may combine a cellular radiotelephone with dataprocessing; a personal digital assistant (PDA) that can include aradiotelephone or wireless communication system; a laptop; a camera(e.g., video and/or still image camera) having communication ability;and any other computation or communication device capable oftransceiving, such as a personal computer, a home entertainment system,a television, etc.

Although the description is mainly given for a user equipment, asmeasuring or recording unit, it should be understood by the skilled inthe art that “user equipment” is a non-limiting term which means anywireless device or node capable of receiving in DL and transmitting inUL (e.g. PDA, laptop, mobile, sensor, fixed relay, mobile relay or evena radio base station, e.g. femto base station).

A cell is associated with a radio node, where a radio node or radionetwork node or eNodeB used interchangeably in the example embodimentdescription, comprises in a general sense any node transmitting radiosignals used for measurements, e.g., eNodeB, macro/micro/pico basestation, home eNodeB, relay, beacon device, or repeater. A radio nodeherein may comprise a radio node operating in one or more frequencies orfrequency bands. It may be a radio node capable of CA. It may also be asingle- or muti-RAT node. A multi-RAT node may comprise a node withco-located RATs or supporting multi-standard radio (MSR) or a mixedradio node.

The various example embodiments described herein are described in thegeneral context of method steps or processes, which may be implementedin one aspect by a computer program product, embodied in acomputer-readable medium, including computer-executable instructions,such as program code, executed by computers in networked environments. Acomputer-readable medium may include removable and non-removable storagedevices including, but not limited to, Read Only Memory (ROM), RandomAccess Memory (RAM), compact discs (CDs), digital versatile discs (DVD),etc. Generally, program modules may include routines, programs, objects,components, data structures, etc. that perform particular tasks orimplement particular abstract data types. Computer-executableinstructions, associated data structures, and program modules representexamples of program code for executing steps of the methods disclosedherein. The particular sequence of such executable instructions orassociated data structures represents examples of corresponding acts forimplementing the functions described in such steps or processes.

The embodiments herein are not limited to the above described preferredembodiments. Various alternatives, modifications and equivalents may beused. Therefore, the above embodiments should not be construed aslimiting.

Abbreviations

-   3GPP 3^(rd) Generation Partnership Project-   ACK Acknowledgment-   AL Aggregation Layer-   ARQ Automatic Repeat Request-   CA Carrier Aggregation-   CC Component Carrier-   CCE Control Channel Elements-   CFI Control Format Indicator-   CRC Cyclic Redundancy Check-   C-RNTI Cell-Radio Network Temporary Identifier-   DFT Discrete Fourier Transform-   DL Downlink-   eNB Evolved Node B-   GSM/EDGE Global System for Mobile communications/Enhanced Data rate    for GSM Evolution-   HARQ Hybrid ARQ-   LTE Long Term Evolution-   NACK Non-Acknowledgment-   OFDM Orthogonal Frequency-Division Multiplexing-   PCC Primary component carrier-   PCell Primary cell-   PDCCH Physical Downlink Control Channel-   PDSCH Physical Downlink Shared Channel-   PRACH Physical Random Access Control Channel-   PRB Physical Resource Block-   PUCCH Physical Uplink Control CHannel-   PUSCH Physical Uplink Shared CHannel-   RACH Random Access Control Channel-   RA Random Access-   RA-RNTI Random Access-Radio Network Temporary Identifier-   RB Resource Block-   RAN Radio Access Network-   RF Radio Frequency-   RNTI Radio Network Temporary Identifier(s)-   RRC Radio Resource Control-   SCC Secondary Component Carrier-   SCell Secondary cell-   SRS Sounding Reference Signal-   TA Timing Advance-   TR Timing Reference-   TC-RNTI Temporary Cell-Radio Network Temporary Identifier-   UE User Equipment-   UL Uplink-   UMB Ultra Mobile Broadband-   VRB Virtual Resource Block-   WCDMA Wideband Code Division Multiple Access-   WiMax Worldwide Interoperability for Microwave Access

What is claimed is:
 1. A method in a user equipment for adjusting atransmit timing of uplink transmissions to a network node in atelecommunications system, the user equipment configurable with aplurality of aggregated serving cells grouped into one or more groups ofserving cells, each of the one or more groups of serving cell sharing acommon timing advance value, each of the one or more groups of servingcells comprising a timing reference serving cell, wherein each of theone or more groups of serving cells uses reception timing of a downlinktransmission from the corresponding timing reference serving cell as areference for the transmit timing of uplink transmissions for thecorresponding aggregated serving cells, the method comprising:identifying a second timing reference serving cell in a group of servingcells, the second timing reference serving cell being different from afirst timing reference serving cell currently being used as the timingreference serving cell defining a common uplink transmit timing foruplink transmissions for each of the aggregated serving cells in thegroup of serving cells; and responsive to identifying the second timingreference serving cell, changing the common uplink transmit timingresponsive to a reception timing of a downlink transmission received atthe user equipment from the second timing reference serving cell byapplying an incremental adjustment to the common uplink transmit timing,wherein said applying the incremental adjustment comprises graduallyapplying two or more adjustments to the common uplink transmit timingfor uplink transmissions for each of the aggregated serving cells in thegroup of serving cells comprising the first and second timing referenceserving cells.
 2. The method of claim 1, wherein, in response to amagnitude of a difference between reception timings of downlinkreception transmissions of the first timing reference serving cell andthe second timing reference serving cell being above a threshold, amagnitude of the incremental adjustment is less than the magnitude ofthe difference between the reception timings of downlink receptiontransmissions of the first timing reference serving cell and the secondtiming reference serving cell.
 3. The method of claim 1, wherein theidentifying comprises receiving a triggering event based on at least onetriggering rule.
 4. The method of claim 3: wherein the at least onetriggering rule is based on a timing threshold; and wherein thetriggering event is provided when an adjustment in uplink transmittiming in response to the second timing reference serving cell wouldcause a change that is greater than or equal to the timing threshold. 5.The method of claim 1, wherein the applying comprises: choosing anactivated secondary serving cell with a lowest index value as a newtiming reference serving cell; and applying the incremental adjustmentwith respect to the activated secondary serving cell with the lowestindex value.
 6. The method of claim 1, further comprising: receiving atleast one parameter associated with the incremental adjustment; andutilizing the at least one parameter in the applying of the incrementaladjustment.
 7. The method of claim 6, wherein the at least one parametercomprises: a maximum amount of magnitude in an uplink transmit timingchange per increment; and/or a minimum aggregate uplink transmit timingadjustment rate; and/or a maximum aggregate uplink transmit timingadjustment rate.
 8. The method of claim 1, wherein the identifying thesecond timing reference serving cell comprises changing the timingreference serving cell for the group of serving cells from the firsttiming reference serving cell to the second timing reference servingcell.
 9. A user equipment adapted to adjust a transmit timing of uplinktransmissions to a network node in a telecommunications system, the userequipment comprising: processing circuitry configured to: identify asecond timing reference serving cell in a group of serving cells sharinga common timing advance value, the second timing reference serving cellbeing different from a first timing reference serving cell currentlybeing used as the timing reference serving cell defining a common uplinktransmit timing for uplink transmission by each of the aggregatedserving cells in the group of serving cells; responsive to identifyingthe second timing reference serving cell, change the common uplinktransmit timing responsive to a reception timing of a downlinktransmission received at the user equipment from the second timingreference serving cell by apply an incremental adjustment to the commonuplink transmit timing, wherein said applying the incremental adjustmentcomprises gradually applying two or more adjustments to the commonuplink transmit timing for uplink transmissions for each of theaggregated serving cells in the group of serving cells comprising thefirst and second timing reference serving cells.
 10. The user equipmentof claim 9, wherein the processing circuitry is further configured toreceive a triggering event based on at least one triggering rule. 11.The user equipment of claim 10: wherein the at least one triggering ruleis based on a timing threshold; and wherein the triggering event isprovided when an adjustment in uplink transmit timing in response to thesecond timing reference serving cell would cause a change that isgreater than or equal to the timing threshold.
 12. The user equipment ofclaim 9, wherein the processing circuitry is further configured tochoose an activated secondary serving cell with a lowest index value asa new timing reference serving cell; and apply the incrementaladjustment with respect to the activated secondary serving cell with thelowest index value.
 13. The user equipment of claim 9: furthercomprising radio circuitry configured to receive at least one parameterassociated with the incremental adjustment; wherein the processingcircuitry is configured to utilize the at least one parameter in theapplication of the incremental adjustment.
 14. The user equipment ofclaim 13, wherein the at least one parameter comprises: a maximum amountof magnitude in an uplink transmit timing change per increment; and/or aminimum aggregate uplink transmit timing adjustment rate; and/or amaximum aggregate uplink transmit timing adjustment rate.
 15. The userequipment of claim 9, wherein the processing circuitry is furtherconfigured to identify the second timing reference serving cell bychanging the timing reference serving cell for the group of servingcells from the first timing reference serving cell to the second timingreference serving cell.
 16. A method, in a network node, for determininginformation for adjusting a transmit timing of uplink transmissions of auser equipment in a telecommunications system, the method comprising:determining adjustment information for an incremental adjustment of acommon uplink transmit timing for uplink transmissions to serving cellsin a group of serving cells sharing a common timing advance value, theincremental adjustment comprising a change from a first timing referenceserving cell for the group of serving cells to a second timing referenceserving cell different from the first timing reference serving cell onwhich a timing reference is currently based, wherein the incrementaladjustment comprises two or more adjustments gradually applied to thecommon uplink transmit timing for uplink transmissions for each of theaggregated serving cells in the group of serving cells comprising thefirst and second timing reference serving cells; and transmitting theadjustment information to the user equipment.
 17. The method of claim16, further comprising selecting the second timing reference servingcell as the timing reference serving cell for a group of serving cells.18. The method of claim 16, wherein the adjustment informationcomprises: a request to apply the incremental adjustment of the commonuplink transmit timing; or a notification that a new timing referenceserving cell is being utilized.
 19. The method of claim 16, wherein theadjustment information comprises a selected new timing reference servingcell.
 20. The method of claim 16, wherein the adjustment informationcomprises at least one parameter, the at least one parameter comprising:a maximum amount of magnitude in an uplink transmit timing change perincrement; and/or a minimum aggregate uplink transmit timing adjustmentrate; and/or a maximum aggregate uplink transmit timing adjustment rate.21. A network node for determining information for adjusting thetransmit timing of uplink transmissions of a user equipment in atelecommunications system, the network node comprising: processingcircuitry configured to determine adjustment information for anincremental adjustment of a common uplink transmit timing for uplinktransmissions to serving cells in a group of serving cells sharing acommon timing advance value, the incremental adjustment comprising achange from a first timing reference serving cell for the group ofserving cells to a second timing reference serving cell different fromthe first timing reference serving cell on which a timing reference iscurrently based, wherein the incremental adjustment comprises two ormore adjustments gradually applied to the common uplink transmit timingfor uplink transmissions for each of the aggregated serving cells in thegroup of serving cells comprising the first and second timing referenceserving cells; and radio circuitry configured to transmit the adjustmentinformation to the user equipment.
 22. The network node of claim 21,wherein the processing circuitry is further configured to select thesecond timing reference serving cell as the timing reference servingcell for a group of serving cells.
 23. The network node of claim 21,wherein the adjustment information comprises: a request to apply theincremental adjustment of the common uplink transmit timing; or anotification that a new timing reference serving cell is being utilized.24. The network node of claim 21, wherein the adjustment informationcomprises a selected new timing reference serving cell.
 25. The networknode of claim 21, wherein the adjustment information comprises at leastone parameter, the at least one parameter comprising: a maximum amountof magnitude in an uplink transmit timing change per increment; and/or aminimum aggregate uplink transmit timing adjustment rate; and/or amaximum aggregate uplink transmit timing adjustment rate.